Yeah, Kiv does actually say to do File -> New Other Miner in the OP, but I missed it the first time as well.
Doesn't matter on my side, no matter what I do, phoenix just won't give me any better results than poclbm, even with phatk. Maybe I'm close to the limit I could get already and there's just no headroom, dunno. Glad it's boosting power for some of you guys though.
I think there are some thing you messed up.
I always go same cards in a single pc.
Since you have different cards, you must have installed different catalyst from 10.10 to 11.5.
Install only one catalyst version to all cards. For this go for safe side. Install 11.5 & 2.4 for all the cards.
Uninstall all catalyst drivers & take out all cards.
Put highest card first, thats 6000 series, 6950 & install catalyst.
In catalyst install only these 3 only.
ATI display driver, ATI catalyst install manager, APP 2.4 & if required vc++.
If you have installed by selecting express, uninstall everything & go by custom.
The catalyst control center v1 or v2 completely messes with settings given by other softwares.
It silently kills the setting from Afterburner & uses its own setting, which won't allow you to get more hash & it will always say that card is over clocked, but it doesn't OC.
Then put another card & install above catalyst again & repeat it for all cards.
In MSI Afterburner, go to settings & remove check mark against, "synchronize settings for similar graphics processors"
This makes, you can OC each card individually.
You just have to select the card in the drop down menu above the check box & clicking ok, you will see, everything changed in main window of Afterburner.
I am also getting lot of stales in slush pool, while in others very few. This is not fault in GUIMiner, may be its due to slush so far not supporting LP.
I have another pc & in that 2 cards are running now, both are 5870 & both mining at 430+ Mhash/s using GUIMiner.
In cmd prompt, also i got the same speed using phatk.
Just tweak around & you will get more hash.